Trocars are pointed surgical instruments which puncture tissue to obtain access to body cavities. Inherent in such instruments is a danger that after the intended puncture, the piercing tip of the obturator (the removable shaft used to pierce the tissue) of the trocar will inadvertently puncture unintended tissue, vessels or organs.
Various techniques for avoiding this inadvertent puncturing are known in the prior art. In U.S. Pat. Nos. 4,601,710 and 4,654,050 the trocar obturator tip is shielded by a sleeve which extends around the point of the obturator after piercing is complete. This technique requires that something project beyond the piercing point of the obturator and requires the addition of a separate shielding element. U.S. Pat. Nos. 4,601,710 and 4,654,030 provide tubes which provide a passage extending into the body cavity after the obturator is removed. However, a shielding sleeve, in addition to these tubes, is required in these devices. This increases the bulk of the trocar and adds to the complexity of its mechanism.
U.S. Pat. No. 4,535,773 discloses the shielding of the piercing tip of an obturator of a trocar through either the interposition of an extensible shielding sleeve, or the retraction of the obturator into the cannula (the tube remaining in the incision after removal of the obturator). The latter arrangement relies upon a solenoid operated detent which holds an obturator in the extended position relative to the cannula and requires electronic sensing means in the tip of the obturator to activate the detent for release. This sensing means requires an electronic alarm network.
The present invention provides advantages over the devices discussed above in that the piercing obturator tip is retracted into a cannula upon completion of insertion of the trocar through the tissues of interest. However, a protecting sleeve extending beyond the end of the cannula into the cavity of the organ is not required.